Voice frequency carrier telegraph



Aug. 13, 1925. 1,549,849

H. A. 'AFFEL VOICE FREQUENQY CARRIER TELEGRAPH Filed Nov. 14, 1922 s sheetg sheet 1 IN V EN TOR.

BY We. A TTORNEY Aug. 18, 1925.

H. A. AFFEL VOICE FREQUENCY CARRIER TELEGRAPH 5 Sheets-Sheet 5 ed Nov. L4, 192?,

V INVENTOR. l? 4 RQQ ATTORNEY Patented Aug. 18, 1925.

UNITED STATES'PATENT OFFICE.

i HERMAN A. AFFEL, F BROOKLYN, NEW YORK, ASSIGNOR T0 AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF YORK.

VOICE FREQUENCY CARRIER TELEGRAPH Application filed November 14. 1922. Serial no. 600,958.

To all whom it may concern:

Be it known that'I, HERMAN A. AFFEL, residing at Brooklyn, in the county of Kings and State of New York, have invented cer- 5 tain Improvements in Voice Frequency Carrier Telegraphs, of which the following is a specification.

This invention relates to multiplex telegraphy and more particularly to the transmission of telegraph signals by so called carrier currents.

In general it is the purpose of the invention to provide arrangements whereby long distance telephone" lines may be utilized to great. advantage for telegraph purposes and accordingly in the arrangements of the invention the carrier frequencies utilized for transmitting the telegraph signals are-within the voice range. Long distance telephone lines are by their very nature, as designed for telephone use, elficientfor the transmission of carrier frequencies within the voice range, but inefiicient, because of the cut-ofis at the upper and lower end of the range, for

i elude cable circuits asa portion thereof, or

which included loaded circuits, as such circuits would have very great attenuation for frequencies outside of thevoice range but would readily transmitthe voice frequencies. Accordingly, there would normally exist on long distance telephone lines a carefully carved p which the transmission efliciency is high and the invention'in its broad aspect consists in utilizing thegood transmission path thus formed for the transmission of a plurality of carrier telegraph channels within ,the voice frequency range. v The ordinary carrier system, which utilizes frequencies relatively hi her than voice frequencies, cannot be applie to'the average type of long distance telephone line because of its transmission characteristics pointed out heretofore and accordingly the use of such would eitherhave to be restricted to 0 en wire lines or, to p ci l lines construe at frequencies withoutv the voice range. This.

cut; range of frequencies within.

be utilized for telegraph purposesin accord-- great expense. By utilizing voice frequency carrier currents this invention makes it possible to utilize practically any of the types of lines at present in existence without the necessity for any change in their equipment and apparatus. Accordingly it" affords a new field of usefulness for existing telephone circuits in that without substantial change they may be utilized to great advantage for multiplex telegraphy. Furthermore the arrangements of the invention provide the advantage of great flexibility'in plant and equipment as the voice frequency carrier telegraph apparatus can readily be switched from one line to another in much the same way as is done in the ordinary telephoneuses ofthe lines. Other features and objects of the invention will appear more fully from the detailed description hereinafter given. a

The invention may be more fully understood from the following description together with the accompanying drawing in the lres of which-the invention and its a plication are illustrated. In Figure 1 t e invention is illustrated schematically as associated with various types of telephone lines such as atwo wire line, a. four wire circuit, and a radio transmitting, and receiving set. In Figs. 2, '3 and 4 are shown curves illustrating graphically the trans mission characteristics of the telephone lines suitable for usewith this invention and the position of the voice frequency carrier chan nelswith respect to said curves. Figs. 5, 6, Y

.7, 8,9, 10, 1.1 and 12 show various types of telegraph currents which may be used in the system of the invention. Figs. 13 and 14 when taken together illustrate in detail circuit arrangements suitable for a. system embodying the invention.

In Fig. 1 is shown a plurality of types telephone transmision lines which may ance with the arrangements of this invention. The line L illustrates the well known type of four wire circuit consistin of two one way circuits for transmission in either direction. These circuits would include apparatus especially designed for the efiicient transmission of voice uency currents. such as repeaters, shown schematicall as A. These circuits would terminate in a ybrid coil and switching arrangements, such as jack J.,. Lines L and L illustrate sending and receiving circuits of a radio system.

' These lines would include apparatus, such as A designed to be highly eflicient for currents within the voice frequency range and are shown terminating in the switching arrangements, such as jacks J 5 and J The line L illustrates atwo way two wire circuit including apparatus, such as .A,, \which might be vacuum tuberepeaters, and terminates in the jack J While the apparatus A in the various lines might be repeater apparatus, it is understood that it may include any type of intermediate circuit or apparatus which would cause the line to have transmission characteristics highly eflicient for currents within the voice frequency range and rents outside of said range. The telegraph arrangements comprise the jacks J J J and J Jacks J and J, may be termed the transmitting jacks and with them are associated a plurality of voice frequency carrier transmitting sets. It has been found in practice that a desirable number of carrier channels within the voice frequency range is ten and hence ten sets of apparatus have been illustrated, although it is to be understood that this number may be varied as desired. The carrier transmitting sets are numbered 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 and 'each set iscontrolled by a key,'such as K. The carrier frequencies of these sets are within the voice frequency range and of suflicient difi'eren'ce toavoid interference with each other. The specific arrangements of the sets will be shownin more detail, hereinafter.- Associated with the jacks J, and J which may be termed receiving jacks, are a plurality of voice frequency carrier recervlng sets termed 1,

2', 3', 4, 5', 6', 7', 8, 9', and 10' which are adapted to receivethe telegraph signals set out from the transmitting sets similar to 1, 2, 3, 4:, 5, 6, 7, 8,9, and ldrespcctively. Each of the carrier receiving sets would be associated-with a telegraph sounder, or other suitable receiving apparatus, such as B.

" The telegraph: apparatus may be associated with the various types of lines by means of a link circuit C.

, Figs. 2, 3 and 4 are curves illustrating graphically the transmission characteristics of the usual types of telephone lines. The

it will be seen that during the voice I'IQf q y ge this loss is low and relatively.

the lines would;

constant. In other weds have high transmission. qualities -'for the voice range of frequencies and this range is well defined. It is inthis range that the carrier telegraph channels are to be open inefficient for cu'r- .with the reversed current.

channels, five in one direction and five in the other, as shown in Fig. 4: by the arrows.

The invention may be more readily understood from a brief consideration of the optional transmission methods of operating direct current telegraph systems. In general, this operation may be eitected by one of three methods. One of these may be termed the single battery or neutral method,

which is provided in asimple series circuit of key, battery, and relay. When the key is closed current flows on the line and when the key is open no current flows. The relay provided is of the so-called neutral type furnished with a retractile spring to return the armature to a neutral position when no current flows. The line currents in a typical case of operation of this kind would be as illustrated in Fig. 5. Another method of operation is that utilized on so called du plex systems. In these systems the spacing signal, i. e. key open, is provided by a current reversal instead of current interruption,

so that it is necessary to employ a polar relay at the receiving terminal. A- relay of this kind provides an armature which rests on one contact with the coil current flowing in one direction and on the opposite contact In this case it will'be noted thatenergy exists on the line at substantially all times to approximately the same degree. The line currents in a case of this kind would appear, for example, as illustrated. in Fig. '6. Another method ofoperation which has been utilizedin certain' cases is the direct current suppression method in which by means of transformers in the circuit or otherwise, the SteadySt-ate or direct current component of the telegraph signal is eliminated or partially eliminated and there remain for operating polar relays the transient pulses or kicks which normally, if the transformers were inserted between the key, battery and relay circuit, would providea-pulse of a certain polarity during the establishment of a current when the key was closed and a pulse of'the reversed polarity when the key was open and thecurrent died down. In Fig. 7 is illustrated the relay current which would flow in a case of this kind when the direct current component is partially suppressed. In such acase the adjustment of the relay armature would be such as to provide its remainingonfeither contact, depending on the'polarity of the preceding pulse. The

advantage of this method of operatioiris that-it provides a stability of signal quality more independent of line current variations I than in other methods. In Fig. 8 is shown the relay current which would flow in a case of this kind when the direct current component is completely eliminated. In Fig. 9 is illustrated the typical line currents which would exist in the case where an ordinary carrier current" was definitely interrupted to form dots and dashes or in other words when the carrier current is modulated by a current such as shown in Fig. 5. In Fig. 10 are shown the carrier "currents in a polarized system using ourrent reversals as the basis of signaling modulation. In this case the current such as shown in Fig. 6 would be utilized to modulate the carrier fre uency to obtain the ourrent as shown in ig. 10. In such a case the reversal of current in the modulating input results in the necessary reversal of current in the demodulator output circuit. This action of signal current reversal manifests itself on the carrier frequency line substantially as the reversal of a phase, as shown in Fig. 10, of what, after'the circuit had reached a practically steady state condition, a

is essentially the carrier frequency itself. The energy on the line in this case will, as in the direct current method noted above, be practically. constant during the entire period of signaling.

In the arrangements of this invention 1nstead of applying the simple current re versal method of operation noted above, it is proposed that the direct current suppression system be used in signaling by acarrier suppression type of system with the objectthat line currents of any appreciable degree will exist only during the periods of making and breaking the circuit. The line currents in such a case would be as shown in Figs. 11 and 12. arrangement would be that the average line current and consequent repeater loading for the case of a number of such carrier channels applied on a single pair of wires would be considerably minimized.

In Figs. 13 and 14, when taken together, there is illustrated in detail the carrier transmitting and receiving. sets and the circuit arrangements therefor of the invention. Two station's, X and Y, are shown interconnected by a two wire line L and transmitting and receiving sets are shown at both stations. Like numerals with the .added designation of prime have been utilized to denote parts at one station similar to parts at another station. The carrier transmitting and receiving sets of these arrangements are constructed to operate on,

the direct current suppression method heretofore referred to. Some of the sets operate to completely suppress the direct current component while others operate to partially suppress it as will be pointed out hereinafter. At station X the line L terminates in the The advantage of such an harmonics thereof will be over circuit 19 and the 400 cycle component will be picked out therefrom and balancing network N and the has coil ting circuit 22- over which. the messages transmitted from station X are sent to line L. Associatedfwith'coil 23 isthe receiving,

circuit 38 over whichthe messages from 23. Associated with coil 23. is the transmit Q lineL are received. Associated with tran'smitt-ing circuit 22 is a transmitting'set comprising thefilter F,, the modulator M and the direct current telegraph circuit 27 ,The filter F is of the type illustrated in the- U. Srpatent to G. A. Campbell, No. 1,22'l', 113, May 22, 1917 and is desi ned to allow the transmission of a band'o frequencies, which for purposes of illustration may be within the range of 350 to 450' cycles. The modulator M is of the duplex vacuum bulbtype illustrated in the U. S. Patent to J. R.

Carson No. 1,343,307. The direct current.

be termed 400 cycles, supplied from the cir- 7 cuit 24. This carrier current, which will be of the typeillustrated in Fig. 12, will be transmitted through filter F and over circuit 22to line L and thence to station Y. The carrier channel of 400 cycles supplied from circuit 24 to the modulator is produced in the following manner. Circuit 24 is made resonant/by the apparatus 25 to a frequency of 400 cycles and is associated with the base frequency circuit 19. The

base frequency circuit 19 is associated with a circuit 15 comprisinga source 16 of a basic frequency of '200 cycles and a vacuum tube 17 arranged to operate as an oscillator. Interconnecting circuits 15 and 19 is a circuit including a vacuum tube 18 adapted to function as a harmonicproduoer. Accordingly a basic frequency of 200 cycles-and transmitted over-circuit 24. By the above arrangements a carrier channel. within the 400 cycles, is supplied for telegraph messages.- Another transmitting set is shown connected to the circuit 22. This set com-.

prises the filter F modulator M and direct current telegraph circuit 34 controlled by relay 35. This set is substantially similar to the one heretofore described except that the direct current telegraph cirtransmitted 'voice frequencyrange, as for example ioo supplied to the modulator M from the cir.

cuit 31. This carrier current is shown for purposes of illustration as of a frequency of 600 cycles. that this frequency value may be different if desired. The frequency would nevertheless be within the voice range and sufficiently different from the other channels to avoid interference. This carrierfrequ'ency of 600 cycles, in circuit 31 is supplied from the base frequency circuit 19. By means of the apparatus 32 circuit 31 is made resonant-at this frequency and is connected to circuit 19. As has been pointed out the base frequency circuit- 19 has continuously transmitted thereover the basic frequency of--20.0 cycles and harmonics thereof. Accordingly the 600 cycle component may be picked out therefrom and transmitted over circuit '31 to themodulator. The band filter F will be designed to readily transmit frequenciesbetween 550 and 650 cycles. Other'trans mitting sets similar to the types illustrated may be connected to circuit 22 and to the base frequency circuit 19 as desired. The carrier frequencies would be within the voice range and would differ from the other channels already in use to avoid interference. In this manner a plurality of channels Within the voice range may be provided and connected to telegraph apparatus toafiord' multiplex transmission over line L.

At station Y the line L terminates in the net work-N and the hybrid coil 23 with which are associated the transmitting circuit 22 and the receiving circuit 38'. Connected to receiving circuit 38 is a receiving set comprising the filter F the demodulator DM and the telegraph receiving circuit 29, the latter being connected to the output of the demodulator and including receiving apparatus herein shown as the relay 30. -This receiving set is adapted to receive the messages sent over the carrier channel of 400 cycles and hence the filter F will be adapted to pass a band of frequencies between 350 and 450 cycles. The

emodulator DM which may be of the dulex vacuum tube type illustrated in the S. Patent .No. 1,343,308 to J. R. Carson, will accordingly be supplied with a carrier frequency of 400 cycles from the circuit 2 1'. In a' carrier suppression system of this type synchronism of the carrier currents at 'both of the terminal sta- It is pointed, out,,however,

current telegraph circuit 27 tions is required both as regards phase and frequency. In other words the carrier current supplied from circuit 24: to demodulator DM must be substantially identical with the carrier current supplied from circuit 24= to the modulator M Accordingly at station Y there is provided a base frequency. circuit 19 and circuit 24: is connected thereto through the apparatus 25'. Apparatus 25 will be resonant at 400 cycles for reasons pointed out hereinafter. Circuit 19 is connected through circuit 20 to circuit 22. Circuit 20' includes the vacuum tube apparatus 21' adapted to function as a harmonic producer. In the .circuit 20' is also included the filter F adapted to transmit frequencies of the order of the basic frequency heretofore referred to as 200 cycles. At the station X is provided the circuit 20 which interconnects the base frequency circuit 19 with the transmitting circuit .22. 'Circuit 20 includes the filter F adapted to transmit frequencies of the order of the; basic frequency of 200 cycles. The

circuit 20 is made resonant at this frequency by the apparatus 21. .Accordingly current of the basic frequency of 200 cycles generated from circuit 15 at station X will be will both be supplied from the same source' andwill be in 'synchronism.

At station Y is provided a transmitting set for the 400 cycle channel. This set is substantially similar to the 400 cycle transmitting set at station X and comprises the filter F the modulator M and the direct The circuit 27' may be controlled by relay 28 and is associated with the input of modulator M by the transformer 26". The filter F connects the output of the modulator to the transmitting circuit 22' which in turn is associated with line L through transformer 23'. At station X there is provided a receiving station for this last mentioned transmitting set. This receiving set is substantially similar to the 400 cycle receiving set already described with respect to station Y and comprises the filter F, the demodulator DM and the telegraph circuit 29. The filter F is connected to the receiving circuit 38 and is adapted to pass a band of frequencies between 350 and 450 cycles. The output of the demodulator DM is connected v 600 cycle channel is transmitted. The filter 7 F is connected to the input of demodulator to the telegraphfcir cuit 29 which may include receiving apparatus herein-shown as therelay30. f

In order to receive the messages sent 2 out from station'X over the 600 cycle channel heretofore referred to there is provided at station Y a receiving set comprising the' filter F,,', the demodulator DM,-, and the telegraph circuit 36. The filter F is adapted to'pass a band of irequenc'ies be tween '550 and 650 cycles and is connected.

to the'receivin'g circuit 38' over which the DM, and the output of .the demodulator is connected to the: telegraph circuit36, which may include receiving apparatus herein shown as the relay 37 The demodulator DM, is supplied with a frequencyiof 600 cycles from the circuit 31" which is 0011-. nected to the base frequency circuit 19 and made resonant at this frequency by the apparatus 32'. f 1 x A transmitting set-suitablefor transmitting messages over a 600 cycle channel is provided'at station Y and is substantially similar to that alread described with respect to stationX. his transmitting set comprises the direct current telegraph circuit- 34 a connected. through an autotransformer, 33 to a modulator M in the manner shown. The modulator will beconnected to the output circuit 22 and thence to line L Y through a filter F4 adapted to transmit a band of frequencies between 550 and 650 cycles. Likewisethere will be provided at station 'X a 600 cycle receiving set to receive the messages from this last mentioned transmitting set. This receiving set is similarto those heretofore described and comprises the filter F the demodulator DM and the telegraph circuit 36 connected in the manner shown. .While only two voice frequency channels are herein illustrated and referred to additional channels may be utilized by the provision at stations X and. Y of additional transmitting and receiving sets similar to those shown and connected in the circuit in a similar manner.

It is pointedout thatin the arrangements of Figs. '13 and 14 each station is utilizing the same channel frequency for transmitting. For example at station X the transmitting-channels are 400' cycles, 600 cycles, etc., and at station Y the transmitting channels are also 400 cycles, 600 cycles, etc. Simultaneous transmission cannot however take placebetween corresponding transmitting sets at both of the stat-ions unless the line circuit is practically perfectly balanced in the hybrid coil network circuit 23. Ten

one way channels between stations may of course be provided in a A-Wire circuit with the channels positioned as shown in Figs. 2 and 3. In order to provide for simultaneous transmission between corresponding transmitting sets in an ordinary two wire circuit without relyingon balance, a slight rearrangement of the transmitting frequencies would have to take place. The transmitting frequencies utilized .at station X might be 400, 600, 800, 1000 and 1200 cycles, while those of the corresponding sets at station Y might be 1400, 1600, 1800, 2000 and 2200 cycles as shownin Fig.- 4. Corresponding changes would necessarily have to be made inthe receiving sets and associated apparatus at each station. This would of course limit operation to five duplex channels. Accordingly while the'invention has been illustrated in certain specific arrangements which lare deemed desirable, it isunderstood that it is capable of embodiment ing the combination of a'transmission line designed to be highly elficient for frequencies,

within the voice range, means for impressing on said line for telegraph purposes a plurality of carrier currents of different frequencies within the voice range, means for 1111- p ressing separate telegraph messages on each of said carrier currents, and means to individually detect from said carrier currents signal currents corresponding to said telegraph messages. s

3. The method of simultaneously transmitting a plurality of telegraph messages over a long distance transmission line, which comprises transmitting over said line a pluirequency range, superimposing a telegraph message on each of said currents, and individually detecting from said carrier currents signal'currents corresponding to said telegraph messages.

4. A multiplex transmissionsystem comprising a transmission line interconnecting two stations, a transmitting set at one station comprising means for applying to said line a carrier frequency within the voice range and means for superimposing a telegraph message on said carrier frequency, 'and a second transmitting set at said station comprising means for applying to said line a carrier frequency also within the voice 2. A multiplex signaling system comprisralityof carrier currents within the voice range but different from said firstmentionedcarrier frequency and means. for superimposing a telegraph message on said carrier frequency, and receiving sets corresponding to each transmitting set, each receiving set including a detector for detecting from the corresponding carrier current signal currents corresponding to the telegraph message superimposed on the carrier current.

5. A transmission line, a plurality of sources of single frequency carrier currents all within the voice frequency range, means to modulate current from each of said sources in accordance with telegraph signals individual thereto, a band filter individual to each carrier current connected between said modulating means and said transmission line to transmit said modulated currents to said line, and means for individually detecting from said carrier currents signaling currents corresponding to said telegraph signals.

In testimony whereof I have signed my name to this specification this 11th day of November 1922. v

HERMAN A. AFFEL. 

